Medical apparatuses and industrial apparatuses, which diagnose a photographic subject using X-rays, use an X-ray tube device as an X-ray source. It is known that a food production line, for example, employs a continuous non-destructive inspection which uses X-rays to inspect any defect in each product.
A device which comprises a container having an X-ray emission window from which X-rays are emitted is well-known as an X-ray tube device used for this kind of inspection. A cathode and an anode, with which electron beams emitted from the cathode collide and from which X-rays are produced, are housed in a cylindrical glass envelope which is kept in a vacuum condition. The glass envelope is fitted into an insulating tube. The insulating tube is immersed in insulating oil which fills the container.